Die bonding is one of the key manufacturing processes in electronic packaging in which a semiconductor die singulated from a wafer is detached and picked from an adhesive dicing tape and then bonded onto a substrate, such as a copper leadframe or a printed wiring board (“PWB”) substrate.
During the die detachment part of the process, a die from a saw-singulated wafer is detached from an adhesive dicing tape using a technique that involves the utilization of a single or a plurality of push-up pin(s) for initiation and completion of the delamination of the die from the dicing tape with the cooperation of vacuum suction holding onto the dicing tape. This technique is commonly adopted for both die bonding and flip chip bonding processes.
Various pin assemblies have been implemented in the prior art to detach a die from an adhesive dicing tape. In a single push-up pin approach illustrated in U.S. Pat. No. 5,755,373 entitled “Die Push-Up Device”, a single push-up pin approach is described in which a push-up pin, in the form of a needle, is fastened to a holder for pushing the die so as to separate the die from the dicing tape held by suction provided by a vacuum assembly. The vacuum assembly is usually held fixed and the push-up needle is independently movable by a raising-and-lowering motor driven mechanism.
When the push-up pin reaches its maximum height, the dicing tape is substantially delaminated from the die leaving only a small contact area supported by the pin. The adhesion of the die to the dicing tape is minimal, so that it is possible to lift the said die up from the dicing tape using a vacuum collet without damaging the die. However, as the size of the die increases in area and its thickness decreases, the single push-up pin approach will be inadequate for successful pick-up.
Alternatively, a two-stage ejection approach illustrated in U.S. Pat. No. 4,850,780 entitled “Pre-Peel Die Ejector Apparatus” attempts to overcome the above problem by providing a telescopic ejector chuck. The telescopic ejector chuck comprises an outer housing surrounded by vacuum suction apertures for pre-peeling the die, and a central housing with a motorized ejector pin connected to an ejector collar for pushing on the die away from the dicing tape so that the die is substantially detached from the dicing tape.
A disadvantage of this two-stage approach is the design complexity of the vacuum-and-spring-loaded telescopic ejector chuck, so that its size has to be relatively large. With its size constraint, the ejector chuck is found to be only effective for die sizes larger than 5 mm. The apparatus is therefore not applicable to semiconductor devices with smaller die sizes.
Another alternative approach is to use different ejector pin configurations to facilitate the die detachment process. This is illustrated in U.S. Pat. No. 6,201,306 entitled “Push-up Pin of a Semiconductor Element Pushing-Up Device, and a Method for Separating”. This approach provides different push-up pins with tip end portions having different profiles that prevent the die from being damaged during die detachment from the dicing tape.
The use of push-up pins with different profiles may have reduced the risk of die damage, but frequent changing of push-up pins with different profiles for new devices may be necessary. Furthermore, if dice of different sizes are to be detached, this prior art does not teach the use of the same tool for these different dice. In addition, it does not cater for re-locating and optimizing the arrangement of the push-up pins for any given die.
A conventional approach to detaching a die from a dicing tape will be described in detail below. FIG. 1A is an isometric view of a push-up pins assembly 100 of the prior art. The push-up pins assembly 100 comprises a plurality of cylindrical push-up pins 102 attached to a plurality of pin mounting holes on a mounting chuck 104. Each push-up pin 102 comprises a tip 105 at one end for contacting the dicing tape during die detachment. The tip 105 is preferably round or tapered so as it will not damage the die when the pin 102 pushes against the dicing tape. A locking ring 106 is disposed on the mounting chuck 104 for locking the push-up pins 102 in position.
FIG. 1B is an isometric view of a die detachment apparatus 110 of the prior art incorporating the push-up pins assembly 100. The die detachment apparatus 110 comprises the push-up pins assembly 100 enclosed by a vacuum enclosure 112.
The vacuum enclosure 112 comprises a flat disc-like top platform 114 having a plurality of openings 116 arranged for the push-up pins 102 to project through and move up and down freely. There are the same number of openings 116 as there are push-up pins 102, and their respective configurations are fixed. When the push-up pins assembly 100 moves up, the push-up pins 102 will correspondingly rise and project their tips 105 above the top platform 114.
The top platform 114 further comprises a plurality of vacuum holes 118 arranged adjacent to the openings 116 for holding the dicing tape with vacuum suction provided by the vacuum enclosure 112 during die detachment. A vacuum seal ring 120 is disposed around the periphery of the top platform 114. The seal ring 120 helps to prevent vacuum leak from an interface between the dicing tape and the top platform 114, thus reinforcing the vacuum suction on the top platform 114.
FIGS. 2A to 2D are cross-sectional views of the die detachment apparatus 110 at various stages of a conventional die detachment process. Referring to FIG. 2A, at the initial stage, a singulated targeted die 122 adhesively attached to a dicing tape 124 is positioned centrally on the top platform 114. Vacuum suction is provided through the vacuum holes 118 thereby holding the dicing tape 124 against a flat top surface 126 of the top platform 114.
At this stage, the push-up pins 102 are located beneath the openings 116 just underneath the top surface 126 of the top platform 114. Meanwhile, a pick-up collet 128 comprising a centrally located vacuum hole 130 in communication with a die pick-up surface 132 is positioned over the targeted die 122.
Referring to FIG. 2B, the pick-up collet 128 has descended and its die pick-up surface 132 lands centrally on the top surface of the die 122. Vacuum suction is provided through the vacuum hole 130 thereby holding the die 122 against the die pick-up surface 132. The die 122 is held securely by the pick-up collet 128 for the rest of the die detachment process.
FIG. 2C is a cross-sectional view of the die detachment apparatus 110 at the third stage of the die detachment process. At this stage, a mechanical upward force is exerted on the back of the die 122 by the push-up pins 102, thereby raising it above the top surface 126 and pushing it away from the dicing tape 124. Simultaneously, the pick-up collet 128 holding the die 122 is elevated by the same distance as the push-up pins 102. Therefore the compressive force acting on the die 122 by both the pick-up collet 128 and the push-up pins 102 is minimized.
The dicing tape 124 is held down against the top surface 126 of the top platform 114 by vacuum suction provided through the vacuum holes 118. Hence, a bending moment induced on the die 122 creates a peeling stress along the interface between the die 122 and the dicing tape 124, thus causing delamination along the interface. The delamination continues as the push-up pins 102 elevate until they reach a predetermined maximum height.
At the end of the push-up action lifting the die 122, the die 122 is held by the pick-up collet 128 and supported only by the tip 105 of the push-up pins 102. The die 122 is substantially separated from the dicing tape 124 with only minimal residual contact area at the tips 105. Hence the adhesion between the die 122 and the dicing tape 124 at these points is very weak.
Referring to FIG. 2D, at the final stage of the die detachment process, the pick-up collet 128 holding the die 122 will stay at the predetermined maximum height for a given delay time, a so-called “pick delay”, before it continues to rise until the die 122 is completely detached from the dicing tape 124.
After the die 122 is completely detached from the dicing tape 124, the push-up pins 102 descend back to their original level underneath the top surface 126 of the top platform 114. The vacuum suction applied to the vacuum holes 118 on the top platform 114 of the vacuum enclosure 112 is then turned off and the dicing tape 124 is unstretched and lies flat on the top platform 114. The collet 128 holding the die 122 will transport the die 122 to a die bonding location before another die detachment process is repeated. In the meantime, another target die will be positioned at the centre of the top platform 114 of the vacuum enclosure 112 to get ready for the next process cycle.
In the die detachment apparatus 110 of the prior art illustrated in FIGS. 1A and 1B, the pattern of the openings 116 on the top platform 114 has to be arranged according to the locations of the push-up pins 102 on the mounting chuck 104. Thus, the openings 116 of the vacuum enclosure 112 and the push-up pins assembly 100 form matching pairs.
When the thickness of a die is more than 0.15 mm, the location of the push-up pins 102 is not as critical, and one arrangement of push-up pins 102 may be applicable for a wide range of die sizes. However, when the thickness of a die is very thin, such as less than 0.15 mm, the arrangement and locations of the push-up pins 102 are critical as incorrect positioning may cause die crack failure during the die detachment process.
The arrangement and locations of the push-up pins 102 underneath the die 122 are especially critical if the die has a thickness of less than 0.15 mm and has a die size of larger than 3 mm×3 mm. When the thickness of the die is reduced further to below 0.10 mm, the accuracy in the locations of the outermost push-up pins 102 from the edges of the die 122 would preferably be within +/−0.2 mm from their optimal locations.
A problem with the push-up pins arrangement of the prior art is that the push-up pins 102 are not allowed to be relocated freely. They are mounted at fixed and predetermined locations on the push-up pins assembly 100 without any option for selectively mounting the push-up pins 102 in other configurations. Thus, re-location of push-up pins 102 is not possible for dice of different sizes that need to be handled by the same apparatus.
The invention seeks to alleviate the aforesaid problem of the prior art by providing a die detachment apparatus wherein the locations of the push-up pins on a push-up pins assembly are not constrained as aforesaid, in order to cater to critical applications such as the detachment of very thin dice of different sizes by using the same apparatus.